1. Field of the Invention
This invention relates generally to vascular interventional medical devices, and more particularly concerns guide wires for use in a therapeutic system or for delivery of medical devices.
2. Description of Related Art
Conventional minimally invasive catheter based therapies typically require guidewires that are one to two meters long extending through a longitudinal lumen in the catheter, and that are torqueable and pushable at the proximal end, yet soft and flexible at the distal end. Many such guidewires are made of stainless steel or the like, and are ground to tapers which provide the desired bending properties along the guidewire. It is useful for such guidewires to be torqueable from the base of the guidewire for manipulation of the distal tip, which is typically bent, for guiding the distal tip through vascular passages. While such guidewires need to be torqueable, pushable and resilient, particularly at the proximal regions of the guidewire, they also need to be flexible, particularly at the distal regions of the guidewire.
One prior guidewire for use with a catheter includes a core wire formed from a nickel titanium alloy, with a tapered distal tip portion and a distal end cap, covered by a sheath of material such as polyurethane, polyethylene, nylon, silicone, polytetrafluoroethylene, cellulose, starch or gelatin. Another prior guidewire comprises a composite guidewire with a core of stainless steel or a nickel titanium alloy, a tapered distal region ending in a distal flexible coil and end cap, also having a major portion of the guidewire covered by a thin layer of polymeric material, such as polysulfones, polyfluorocarbons, polyolefins, polyesters, polyamides, polyurethanes, blends and copolymers such as polyether block amides.
However, there remains a need for a guidewire with enhanced proximal stiffness, with a stiff, high modulus reinforcement, allowing for greater manipulation of the guidewire by the physician, along with greater distal tip flexibility with radiopacity. The present invention meets these needs.
Briefly, and in general terms, the present invention provides an improved composite guidewire with a proximal high modulus reinforcement member for promoting greater proximal stiffness, with a tapered distal region and distal radiopaque coil providing greater distal tip flexibility with radiopacity. The composite structure thus advantageously provides for a composite guidewire with greater resilience, a transition in stiffness, and tip flexibility. The proximal stiffer, high modulus member, covering or reinforcing a nickel alloy core, can be formed of high modulus metals such as stainless steel, titanium, and the like, allowing for greater manipulation of the guidewire by the physician, while the distal coil has enhanced durability, being formed from a composite strand of a nickel titanium alloy and platinum.
The present invention accordingly provides for a composite guidewire having an elongated, flexible core formed from a nickel titanium alloy having proximal and distal regions, with the distal region having a tapered portion, a reinforcement tube disposed over the proximal region of the core, a primary coil disposed over the tapered distal region of the core, with a coating of a heat shrinkable material disposed over at least a portion of the reinforcement member, an intermediate portion of the core, and at least a portion of the primary coil, and a distal tip secured to the distal end of the core.
In a presently preferred embodiment, the core is a nickel titanium alloy rod, although the core may alternatively be formed of one or more elongated strands of nickel titanium alloy, or an elongated tube. In another presently preferred aspect, the proximal reinforcement member is formed as an elongated ground stainless steel hypo tube, although the reinforcement member may alternatively be formed of an elongated tube made of titanium, or a nickel titanium alloy. In another presently preferred aspect, the proximal reinforcement member is formed with a distal tapered portion, to provide for a transition in stiffness of the guidewire. In a presently preferred embodiment, the heat shrinkable coating is formed from an elongated tube of polytetrafluoroethylene (PTFE), although the heat shrinkable coating may also be selected from other heat shrinkable materials such as polyethylene, for example. In another presently preferred aspect of the invention, the distal primary coil is formed from one or more nickel titanium alloy strands or wires, and in another presently preferred aspect the distal primary coil is formed from one or more platinum wires, or a combination of one or more nickel titanium alloy strands and one or more platinum wires. In one currently preferred embodiment, the distal tip is formed of platinum, and is bonded to the distal end of the core such as by welding, or soldering, or the like, although the distal tip may also be formed of other materials such as a tantalum filled epoxy adhesively bonded to the distal end of the core.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.